Air filter



FIG. 1 is a top front and left side perspective view of air filter showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is a bottom plan view thereof.

The broken lines depict portions of the air filter that form no part of the claimed design. 

The ornamental design for an air filter, as shown and described. 